I propose an intensive study of structure-function relationships in occluding junctions and cellular control of their maintenance and modulation. These junctions are vital to tissue cohesiveness, functional polarization, and control of transepithelial permeability in mammary and other transporting epithelia. I intend to determine metabolic requirements for steady-state maintenance and for assembly/disassembly of occluding junctions in cell culture; to identify any morphological changes accompanying induced change in junction permeability; to determine effects of agents that alter membrane fluidity or cortical cytoskeletal-contractile elements; to relate these in vitro observations with normal modulation of mammary junctions in vivo.